1. Field of the Invention
The present invention provides a three-dimensional powder-based production process using powders based on cyclic oligomers, and to moldings produced by this process
2. Discussion of the Background
Rapid prototype production is a recently charged task in many areas of endeavor (e.g., automotives, aerospace, sporting equipment, etc.). Generally, desirable processes are those whose operation is based on pulverulent materials and in which the desired structures are produced in a layer-by-layer manner by selective melting and hardening. In these processes there is no need for support structures for overhangs and undercuts, because the powder bed surrounding the molten regions provides sufficient support. In addition, there is no need for a subsequent operation to remove a support. These rapid prototype production processes are also advantageous in that they are suitable for small-run production.
A disadvantage of components produced from an RP process with thermoplastics of the prior art is that these process have restricted use at relatively high temperatures. By way of example, since most of the machines currently available in the market for the processes cannot be heated above 200° C., the type and nature of materials for use therein is severely restricted. Only thermoplastics whose melting point are up to 200° C., or in some instances up to 220° C., can be used with confidence. Heating of the machines is necessary to prevent the curl effect, which occurs if the construction chamber temperature is too low thus resulting in the uppermost layer of the molten region to bend upward at the edges or even over large areas. If this occurs, the next powder layer cannot be applied without breaking the previously melted regions out of the powder bed and, therefore, layer-by-layer production of a molding is impossible.
The curl effect can be eliminated by heating the entire construction chamber to a temperature just below the melting point of the material therein (crystallite melting point in the case of semicrystalline polymers). Accordignly, with the currently available equipment, it is only possible to process polymers whose melting point is up to 200° C. and in limited circumstances up to 220° C. Accordingly, the components produced therewith have insufficient heat resistance for applications above 120° C. This is particularly problematic in the automobile sector where components have to retain adequate strength even at temperatures above 120° C. in order to fulfill their function.
Therefore, there remains a critical need for the development of a process that permits production of moldings with higher heat resistances, using a processing method having maximum reproducibility, on the machines available in the market or on RP/RM machines with limited preheating (e.g., a maximum of 200° C.).